Effect of Processing Conditions on the Scratch and Mar Behavior of TPO Systems

Abstract

Thermoplastic Olefins (TPO) possessing properties such as low density and recyclability are widely used in the automotive industry as a material of choice for numerous car parts and components. Scratch and mar damage reduces aesthetic value and is highly undesirable. Therefore, it is important to study the scratch and mar behavior of these materials. In this research TPO systems with and without scratch additive were injection molded at temperatures of 40°c, 50°c and 60°c be compared in terms scratch and mar behavior. All scratch and mar tests are administered on samples by a scratch machine using the ASTM standard D7027 method. Scratch behavior was studied using the onset of whitening as parameters judged by human observers and by the Automatic Scratch Visualization (ASV©) software. Visibility analysis of mar tests was done by checking for overall extent of visibility rather than simply the onset, and also by using contrast curves. Grazing incidence angle XRD was used to establish that surface crystallinity increases with mold temperature. Surface roughness results from the LSCM, scratch co-efficient of friction, and FTIR-ATR analysis were used to explain the behavior of scratch additive on the surface. Higher MFR systems show more dependence on mold temperature and show better scratch and mar behavior at higher temperatures. At higher mold temperatures, the scratch additive migrates better to the material, causing scratch and mar tips to slip and have lower co-efficient of friction and therefore, show delay in the onset of scratch and lower visibility for mar.